new oceanic crust
In the oceans, plates move apart at mid-ocean ridges. Lava rises upward, erupts, and cools. Later, more lava erupts and pushes the original seafloor outward. This is seafloor spreading. Seafloor spreading forms new oceanic crust. The rising magma causes the ridge to be buoyant. This is why there is a mountain range running through the oceans. The plates pulling apart cause earthquakes.